Known methods for predicting weight loss fail to account for slowing of metabolism as weight is lost and therefore overestimate the degree of weight loss. While this limitation of the 3500 Calorie per pound rule has been known for some time, it was not clear how to dynamically account for the metabolic slowing. The invention provides a Java applet for modeling of human metabolism to improve the weight change predictions. The model has been validated using previously published human data and the model equations have been published. A web-based implementation of the published dynamic model has been created to allow users to perform simulations for planning weight loss interventions in adults and accounts for individual differences in metabolism and body composition. Values to the user include being able to see whether the target weight loss is realistic when the necessary caloric restriction, exercise and timeframe components are highlighted. Unrealistic goals become apparent. More moderate goals may result in greater long term success. The model also defines the caloric intake to be followed once the new weight target has been met to prevent weight being regained.